Apparatus for controlling the flow of particulate materials normally comprises inwardly converging wall structure defining a throat opening at the lower end thereof, and into which the particulate material is funnelled by the wall structure. Within the throat there is normally located a movable gate for controlling the flow of particulate material through the gate. The apparatus may further comprise superior wall structure to define a containing hopper, and the ensuing description is made with reference to hoppers. However, it should be appreciated that such term is intended to cover apparatus wherein particulate materials are merely piled above a throat without being contained by a superior wall structure. Various types of gates are known, particularly for use with very large hoppers which may, for example, form a ship's hold, and amongst which may be exemplified roller gates and basket gates. It is well known that certain types of particulate material will not flow freely; thus it is found that certain materials, especially where they comprise large lumps, are prone to arch formation in the throat area. Other types of materials, especially fine, cohesive powdery materials, tend to block together, resulting in the formation of rat holes, arches or bridges.
Various expedients have hitherto been adopted or proposed for promoting the flow of particulate materials. Mechanical expedients comprise vibrators and movable members. Whilst certain of these have been found to be more or less suitable for use with specific particulate materials, others have not been found acceptable, primarily due to economic factors. The mechanical expedients may be combined with, or even supplanted by non-mechanical expedients, for example by coating the funnel wall structure to reduce frictional drag, and increasing the flow velocity through the throat opening in the so called bulk flow gate, whereby the energy of the moving material serves to break incipient arch and rat hole formation. However, the bulk flow gate engenders certain difficulty in containing and controlling the material flowing from the hopper.
It is then an object of this invention to provide hoppers with improved flow control means.
It is a further object of this invention to provide hoppers with relatively inexpensive structure for promoting flow through the funnel wall structure of the hopper.
It is a further object of this invention to provide a means for economically converting existing hoppers so as to provide therein improved flow control.
It is a still further object of this invention to provide a hopper wherein the flow rate therefrom may be variable from very high, bulk flow rate to low flow rates.